1. Field of the Invention
This invention is related in general to tutorial devices for classroom and similar activities. In particular, it describes an instructional tool for studying and illustrating interrelationships between the earth, moon, and sun.
2. Description of the Related Art
Since the days of Copernicus and Galileo, teachers have struggled with ways to explain to pupils the interrelationship between the sun, the earth and the moon in simple, easily understandable terms. Even in modern days, basic misconceptions remain about the workings of the sun, moon and earth in creating lunar phases and seasons. For example, even well-educated people commonly believe, incorrectly and in spite of having been taught properly at some point in their lives, that the moon's apparent phases are the result of the earth's shadow upon it. That this is incorrect would be easily understandable and more likely to be remembered if visualized with the aid of a planetary model.
In order to help illustrate the relative motion of the sun, the planets, their moons, and their influence on each other, people have devised tutorial instruments that approximate the relative position of the celestial bodies of interest. One such device is described in U.S. Pat. No. 554,809 to Yaggy (1896). The invention consists of a chart to illustrate the changes in the moon as it travels in its orbit around the earth. A stationary frame with openings through which the sun and earth are illustrated and various rotating structures are employed to display the relative position of the three bodies at different times during their motion through space.
Another, more recent invention is disclosed by Tzeng in U.S. Pat. No. 5,114,348 (1992) to illustrate lunar phases. The device consists of the combination of a stationary base containing rings with moon pictures and calendar information with rotating elements representing the moon and earth's longitudinal positions. The movable elements are used in conjunction with the fixed rings on the base to obtain moon data for selected times and earth longitudes.
These devices are rather complicated and cumbersome, and cannot be used to illustrate the relative position and attitude of each body with respect to the other two as the sun, moon and earth move through space. Therefore, there still exists a need for a simple, inexpensive and easily-operable device suitable for use as an instructional tool. This invention provides a simple apparatus that fulfills this need.